ARS | Publication request: RELATIVE SUSCEPTIBILITY OF PECAN CULTIVARS TO ZONATE LEAF SPOT

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 28, 1996
Publication Date: N/A

Interpretive Summary: Zonate leaf spot of pecan is a disease that appears infrequently but can cause reduced yield and poor fruit quality due to the loss of leaves at a time when the fruit is developing. All pecan cultivars were considered susceptible but no information existed as to the degree of susceptibility. Unusually wet weather during June, July and August of 1994 caused on outbreak of zonate leaf spot in Georgia which enabled 36 different genotypes of pecans to be evaluated for disease resistance. Only 9 of the genotypes were moderately to highly susceptible but three of the leading cultivars grown in Georgia were in that group. This is the first report of degrees of susceptibility in pecan for zonate leaf spot. This information can be used by extension specialists advising pecan growers that are considering cultivar characteristics when establishing new orchards.

Technical Abstract: Zonate leaf spot (ZLS) on pecan--associated with unusually wet weather during June, July and August-- occurred across much of Georgia during the summer of 1994. Scott -Knott cluster analysis indicated that 27 of 36 evaluated genotypes exhibited little or no field susceptibility to ZLS. The 'Moneymaker' cultivar exhibited the greatest susceptibility of all cultivars studied, with 'Cape Fear', 'Elliott', 'Sumner' and 'Sioux' segregating to exhibit moderate susceptibility. An evaluation of commercial orchards indicated that susceptibility of major southeastern cultivars as : 'Desirable' < 'Stuart' < 'Schley' < 'Moneymaker'. Control of ZLS in commercial orchards using standard fungicide spray strategies appeared to be generally ineffective.